In-vivo temperature refers to temperature of tissues in complete and survival individuals. In the biological and medical field, in-vivo temperature measurement methods are divided into invasive measurement and noninvasive measurement. The invasive measurement method is simple, real-time and accurate, and it is convenient to monitor measurement positions by videos. However, problems with the method are that, wound caused by the method is comparatively large, insertion of probes often leads to metastasis of pathological cells, interaction between radiation fields of heating sources and the probes reduces measurement accuracy, and measured temperature is temperature at a certain point, not temperature distribution over a whole coagulation area. The noninvasive temperature measurement method is now widely accepted and used in the medical field as being capable of effectively preventing infection of wound or expansion of cancer cell, and of providing real-time information of in-vivo temperature and temperature (field) distribution images deeply in tissues with comparatively high accuracy.
Presently, the noninvasive temperature measurement method comprises a ultrasound temperature measurement method, a microwave temperature measurement method, a nuclear magnetic resonance (NMR) temperature measurement method, a remote magnetic nanoparticle measurement method and so on.
Limited by size of organisms, the ultrasound temperature measurement method employs reflection echo, and a disadvantages thereof is that it must measure sound and temperature characteristics of different tissues in advance, but temperature characteristics of the tissues is significantly different and unstable. The microwave temperature measurement method can only be used to tumor at superficial layers, and resolution is to be significantly reduced at deep layers. However, this method must predetermine temperature distribution and measure structure and electrical parameters of organisms, this is because that thermal noise microwave measured at body surface is related to temperature distribution, structure of tissues and electrical properties within a measurement range. Problems with the NMR temperature measurement method are that it is too expensive to be widely used, spatial and temperature resolution thereof are limited, and more importantly, it can only obtain variation in temperature, not absolute temperature of tissues. A remote noninvasive temperature measurement method using magnetic nanoparticles is a high-accuracy temperature (field) measurement technique deeply in tissues being capable of addressing the above-mentioned problems. This method implements measurement and control of in-vivo temperature, and thus being capable of assessing and adjusting hyperthermia treatment of tumor in real time at a molecular level. In addition, a magnetic particle imaging (MPI) based on magnetic nanoparticles features an extremely high real-time rate in remote noninvasive in-vivo temperature measurement. Superior to a traditional noninvasive method for in-vivo temperature measurement—NMR, the MPI system is more simple, cost-effective and accurate, and generates pixels by changing magnetization of the magnetic nanoparticles whereby enabling the system to have high temperature sensibility. Therefore, the MPI is capable of measuring and imaging the in-vivo temperature in theory.
Temperature-related attributes of the magnetic nanoparticle comprise a particle size, saturated magnetic moment, concentration distribution thereof in the organism, and so on. The particle size and the saturated magnetic moment can be determined via repeated test outside the organism, but it is difficult to measure concentration of the magnetic nanoparticle in the organism, and no measurement method is available at present. Meanwhile, uncertainty of concentration and spatial distribution of the magnetic nanoparticle in the organism is to cause a significant error in the in-vivo temperature measurement. To summarize, to facilitate remote temperature measurement without knowing concentration of the magnetic nanoparticle has become an unsolved problem in magnetic nano hyperthermia treatment of tumor.